1. Field of the Invention
The present invention relates to an clutch outer which is formed by die-casting to have a cylindrical portion and an end wall leading to one end of the cylindrical portion, and in which slits are defined in the cylindrical portion at a plurality of points circumferentially equally spaced apart from one another to extend in an axial direction of the cylindrical portion so that one end of each slit is closed by a portion closer to the end wall and the other end of each slit opens into the other end of the cylindrical portion, and a plurality of friction plates having engagement claws provided on their outer peripheries are slidably engaged into the slits. The invention particularly relates to an improvement in shape of each slit.
2. Description of the Related Art
Such a conventional clutch outer is known, for example, from Japanese Patent No. 3120291 or the like. The slits are defined in the cylindrical portion at a plurality of circumferential points so that their portions on the sides of inner and outer peripheries of the cylindrical portion of the clutch outer have the same width.
In the multi-plate clutch constructed using such a clutch outer, it is desired that the friction plates are formed of an inexpensive thin iron plate to reduce the cost, and the number of the friction plates is decreased to provide compactness and a reduction in weight. For this purpose, it is necessary to suppress to a small level the surface pressure in contact between the engagement claws of the friction plates and the clutch outer with the engagement claws engaged in its slits, and to minimize the distance between the slits in the circumferential direction of the cylindrical portion of the clutch outer to maximize the number of the slits.
To form the clutch outer by die-casting, portions for forming the slits are provided in any one of a die for forming an inner face side potion of the clutch outer and a die for forming an outer face potion of the clutch outer. A die-parting face in each slit is established at a location flush with the outer peripheral surface or the inner peripheral surface of the cylindrical portion. In the conventional clutch outer, if a draft for the slits is set at a small value when the number of the slits is large, the resistance during opening of the dies is increased and hence, there is a possibility that a galling is generated in a product at a portion corresponding to the die-parting face. For this reason, it is necessary to set the draft for each of the slits at a large value in order to prevent the generation of the galling.
However, if the draft is increased, a relatively large difference is generated between the width of one end of the slit on the side of one end of the cylindrical portion, i.e., on the side of the end wall, and the width of the other end of the slit on the side of the other end of the cylindrical portion. Therefore, the failure of the operation of the friction plates may occur at the one end of the slit having the smaller width, while the engagement claw of the friction plate moves within the slit to generate a striking sound at the other end of the slit having the larger width.
Accordingly, it is an object of the present invention to provide a clutch outer which is designed to prevent the generation of the galling in the product and the generation of the striking sound, and to maximize the number of slits.
To achieve the above object, according to the present invention, there is provided a clutch outer which is formed by die-casting to have a cylindrical portion and an end wall leading to one end of the cylindrical portion, and in which slits are defined in the cylindrical portion at a plurality of points circumferentially equally spaced apart from one another to extend in an axial direction of the cylindrical portion so that one end of each slit is closed by a portion closer to the end wall and the other end of each slit opens into the other end of the cylindrical portion, and engagement claws provided on outer peripheries of a plurality of friction plates are slidably engaged into the slits, wherein each of the slits comprises a wide portion which is defined on the side of an inner periphery of the cylindrical portion and into which the engagement claws are engaged, and a narrow portion defined on the side of an outer periphery of the cylindrical portion with a width in a circumferential direction of the cylindrical portion being smaller than that of the wide portion, the wide portion and the narrow portion being connected to each other through a step facing a radially inward direction of the cylindrical portion; wherein a draft for the wide portion during die-casting is set at a value smaller than a draft for the narrow portion; and wherein a die-parting face in the die-casting is established on the side of the outer periphery of the cylindrical portion.
With such arrangement, each of the slits is formed into a stepped configuration such that its portion on the side of the inner periphery of the cylindrical portion is wider. By setting the draft for the narrow portions of the slits located on the side of the parting face at a relatively large value, it is possible to prevent the galling of a product to the utmost during separation of the product after die-opening. In addition, by setting at a relatively small value the draft for the wide portions, into which the engagement claws of the plural friction plates are engaged, it is possible to prevent the failure of the operation of the friction plates, and the generation of the striking sound. Thus, it is possible to maximize the number of the slits and to suppress the surface pressure of contact between the engagement claws of the friction plates and the clutch outer to a small level. Further, each of the friction plates can be formed of an inexpensive thin iron plate, leading to a cost reduction, and the number of the friction plates can be decreased, leading to compactness and a reduction in weight.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.